Electrical timing circuit



Oct. 26,1937. P. L. HOOVER 2,097,066

ELECTRICAL TIMING CIRCUIT Filed April 4, 1956 n5 Vou- 60 CYC S GIHDVOLTAGE IN VENT OR Wren? Patented Oct. 26, 1937 PATENT OFFICE ELECTRICALTIMING CIRCUIT Paul L. Hoover, Highland Park, N. J., assignor toiEndowment Foundation, New Brunswick, N. 3., a corporation of New JerseyApplication April 4, 1936, Serial No. 72,743

Claim.

This invention relates to an electrical circuit and means for providingelectrical impulses of exact periodicity or frequency which may be usedto operate some mechanism directly or indirectly, as will be hereinafterpointed out.

Many different types of mechanical mechanisms have been used in the pastto operate contacts and thus send periodic electrical impulses through acircuit. Some of these are even capable of speed regulation over alimited range, but the accuracy of this speed calibration is never verygood due to friction and wear on the moving parts of the mechanism.

Certain types of timing mechanisms, including metronomes, have beenbuilt in the past to perform a single duty; that is, to either flashlights, send an electrical impulse through a circuit, or produce audibletones or clicks.

My present invention has for its object, as ch.- cuit arrangement inwhich electrical impulses are produced by the devices in the circuititself, and generally speaking, without any mechanical mov ing elements.

Another object of my invention is to provide means whereby theperiodicity of the impulses may be quickly and conveniently varied toany desired value over a relatively wide range.

Another object of my invention is to provide an electrical timingcircuit in which lights may be flashed, impulses sent through a circuit,or other visible and audible tones or clicks may be produced. This dualpurpose is very useful in certain classes of work, such as thereplacement of metronomes for musical purposes where a combination offlashing light and audible tone is a distinct advantage over the simpleaudible tone given by a mechanical metronome. Furthermore, incallsthenics the audible tone cannot be heard anyway, and the use of aflashing light, alone, as a metronome is very helpful.

These and other objects will be apparent to one skilled in thisparticular art, by a reading of the specification, taken in connectionwith the annexed drawing, wherein:

Figure 1 is a diagram of a circuit arrangement which I have found to behighly useful in connection with the purposes heretofore set forth.

Figure 2 is a curve showing the characteristics of the tube used in thecontrol of the circuit shown in Figure 1.

Figure 3 is a diagram illustrating the kind of signal impulse producedin the circuit for application to the output device.

By reference to Figure 1, it will be seen that when the switch I isclosed, power is applied to the primary 2 of the transformer l6.Secondary winding 4 supplies power to the cathode of rectifier tube 5.Secondary 6 supplies power to the cathode of the discharge tube i5.Secondary l supplies a relatively high voltage, which may be of theorder of 300 volts, to the rest of the circuit. Condensers l and 9,along with choke coil 8, constitute a filter circuit to smooth out thehalf-wavepulses which the rectifier tube 5 passes. The power across thevoltage divider, consisting of resistance l0 and potentiometer ii, isthus direct current. If direct current of the correct value wereavailable, the rectifier part of the circuit just described could beomitted as its sole purpose is to convert the ordinary 115-volt,60-cycle power into direct current power of the required voltage; 1. e.,300 volts, in this case to operate tube I5, which, is a so-calledgridcontrolled gas discharge tube such as an RCA885. The particularfeature of this type of tube, which makes it useful in this application,is that with the grid potential set at some given value, no platecurrent will flow at all until the plate voltage reaches a definitevalue. This plate voltage is known as the breakdown voltage. Figure 2shows the relation between grid voltage and plate breakdown voltage forthe RCA 885 tube. However, once the tube breaks down, and plate currentstarts to flow, the grid loses control and can no longer influence theflow of current through the plate circuit. When the plate voltage dropsbelow a few volts, however, the tube "goes on and the grid then regainscontrol.

From Figure 2, it is seen that the breakdown voltage is practically tentimes the grid voltage. Therefore resistance ill of the voltage dividershould have ten times the resistance of'potentiometer i I. The magnitudeof resistance it! may be of a desired value; preferably, in practice, itmay lie between 10,000 and 50,000 ohms.

As soon, then, as direct-current power is applied across resistance l0,current will start to flow through resistance l2 and charge condenserl3. Since no current can flow through the device ll, shown in Figure 1,as a coil, or tube l5 at the start, due to the fact that the voltage isbelow the breakdown value of tube I5, the charge on condenser l3 willbuild up until the voltage across it is equal to the breakdown voltageof the tube. At this point, then, tube It breaks down and passes currentthrough the plate circuit, with the result that condenser i8 dischargesthrough coil l4 and tube l5, giving a glow-like flash. The time of thisdischarge is very short, of the order of micro-seconds, so it can beregarded as instantaneous. This is shown in Figure 3, where the signalimpulses II are plotted against time and current to illustrate the kindof signal impulse which is impressed on the output device connected inseries with the plate or equivalent element of the tube. As soon ascondenser is is discharged, the voltage across it, and hence the voltageon the plate of tube It, is so low that the tube goes out and the gridregains control again. The cycle then repeats.

. denser to the proper voltage. This, or course, de-

pends on the resistance i2, the condenser l3, andthe setting ofpotentiometer Ii which is the variable that controls the breakdownvoltage of tube l5. By keeping resistance l2 and condenser l3 fixed invalue and changing only potentiometer ii, a range oi almost ten-to-onemay be had for the period of the charging cycles when using the 885tube. It a wider range isrequired, either resistance I! or condenser l3,or both, may be varied.

A very important feature of this circuit is that an increase or decreasein either line voltage or frequency will not change the periodicity ofthe charge and discharge cycles of condenser l3. This is because of thefact that any change in the supply line voltage or frequency would onlychange the magnitude of the direct-current voltage across the voltagedivider elements lii and il. Thus, if the voltage across resistance illincreases, then condenser l3 will be charged at a faster rate, but thevoltage across potentiometer II also increases proportionately so thatthe grid voltage, and consequently the plate breakdown voltage or tubei5, also increases proportionately. This would not be the case if therelation as shown in Figure 2 were not linear.

The output device of this electrical timing means or metronome is shownin Figure 1 in the form of a coil H, but it may be any one or amultiplicity of numerous types of translation devices. For instance,coil l4 may be the operating coil which moves or controls the recordingmechanism of a chronograph. It may be a loud speaker, in which case, theelectrical pulses are converted into sound pulses or clicks. It may bethe primary of a transformer, in which case, the induced voltage in thesecondary may be used to control either high voltage or high currentdevices, depending on the turns ratio of this output transformer. Outputcoil it may also be the operating coil of a relay which controls amultiplicity of contacts, which in turn controls the flow of power in anumber of external circuits. In case it is desired, several output coilsmay be put in series and thus several output devices opdenser beingconnected to at least two of said erated simultaneously. The duelcharacter of this output device may be utilized by having coil it theoperating coil of a relay, and this relay so designed that when therelay armature operates, it closes a pair of contacts in an externalcircuit, flashing a light, and at the same time, the relay armature maystrike a member to produce an audible sound or tone. Where only theflash from the tube is wanted as a signal, the device i4 may be a plainresistance, or it may even be dispensed with.

This type of instrument, utilizing the circuit of Figure 1, has beenfound very useful for musicians, but as heretofore indicated, theinstrument in which the apparatus of the circuit is used, may take anydesired shape and serve other purposes.

Furthermore, the circuit shown in Figure 1 is to be considered as thepreferred form of circuit and not as the only circuit or means wherebyelectrical pulses of exact periodicity may be made to function as ametronome.

What I claim is:

1. An electrical timing circuit for producing spaced short-time impulsesincluding a voltage of said condenser being. connected to a terminal ofsaid divider through said resistance, a gasfilled tube having at least acathode, anode and grid and having a ratio of plate voltage to gridvoltage at break-down which is substantially a constant, an outputdevice connected in series between said plate and the juncture of saidcondenser and resistance, a connection from said cathode to saidintermediate point on said voltage divider, and a connection betweensaid grid and a point on said voltage divider on the other side of saidintermediate point from said firstnamed terminal.

2. An electrical timing circuit for producing spaced short-time impulsesincluding a two-section voltage divider composed of two series-connectedresistances. a condenser and a third resistance connected in seriesacross one section of said divider, one terminal of said condenser beingconnected to the point between said two sections, a grid controlledgas-filled discharge tube having at least grid, cathode and anode andhaving a substantially straight line relation between its grid and platevoltages at breakdown, a connection between said grid and an adjustablepoint on the second 01' said voltage divider resistors, an output deviceconnected in series between the anode and the Junction of said condenserand the third resistance and a connection between said cathode and saidpoint between said two sections.

3. An electrical timing circuit as defined in claim 2, in which thefirst said voltage divider resistance is larger than said secondresistance and in which the ratio of said two resistances is of theorder of the ratio oi! the anode voltageto the grid voltage atbreakdown.

4. An electrical metronome having a circuit for producing and utilizingspaced short-time impulses including a trigger-action tube havingelements comprising at least a grid, a cathode and a plate, a source ofdirect current, a condenser and means for charging the condenser fromsaid source, an output device in series with the plate of the tube forutilizing said impulses, said contube elements, in series with theoutput device, whereby the discharge of the condenser will be throughsaid output device, and means connected to said source of current andalso between the grid and cathode to vary the speed of the impulsesproduced, said condenser and translating means being connected in seriesin the anodecathode circuit.

5. A timing circuit utilizing devices which will electrically producespaced short-time impulses of exact periodicity and use the same througha translating means, with means for adjusting the periodicity over awide range, said devices including a grid-controlled breakdown tube withat least a cathode, and a plate, and having substantially straight-linecharacteristics between its grid and plate breakdown voltages, and acondenser, with means for charging the condenser from a source of directcurrent, said condenser and translating means being connected in seriesin the anode-cathode circuit, and means for applyigg a voltage to saidgrid with respect to said ano e. a

PAUL L. HOOVER. I

